The utilization of low speed, low altitude aircraft for spraying both large and small acreages of field crops and orchards has been widespread in the agricultural industry. Where the size of the field is such as to require a large number of passes of the aircraft over the field in order to provide coverage, difficulty has been encountered by the aircraft operator in insuring that each of his successive passes over the field is spaced precisely with respect to the previously sprayed adjacent path in order to avoid either gaps or overlaps in spraying coverage. On small fields, guiding markers may be employed which are temporarily or permanently mounted along the field and the aircraft operator may align his craft with the guiding markers. This method, however, is entirely impractical where crop lands of several thousand acres in extent are involved so that the cost of installing and maintaining such markers becomes prohibitive. Furthermore, with such large acreages, it is very difficult for the pilot, after he has passed a marker on one end of the field to actually sight the marker on the remote end of the field and to make sure, despite existing wind conditions, that the plane is traveling on a straight line between the two markers.
Radar-type aircraft guidance systems such as used to assist planes in making landings under adverse conditions are obviously far too expensive and complicated to be utilized in an industry characterized by a large number of small companies or individual operators. Furthermore, this type of guidance system would require that the directing beacon be moved laterally after each pass by the aircraft across the field, which again presents an impractical solution to the problem.
Accordingly, the desirability of an economical crop spraying aircraft guidance system that could be carried on the aircraft and requires only simple reflector devices temporarily placed on the ground adjacent the field to be sprayed to indicate the aircraft position at any time relative to the field, is deemed to be obvious.